1. Field of the Invention
The present application is related to an optical viewfinder, and more particularly to an optical viewfinder including a display element disposed in a viewing optical path of the optical viewfinder and to an optical apparatus, e.g., an image pickup apparatus or an observation apparatus, using the optical viewfinder.
2. Description of the Related Art
In order to increase an amount of information to be displayed on an optical viewfinder of a camera, it has recently been generalized to arrange, near a focusing plate positioned in a primary image plane of an imaging lens, a display panel made of a polymer network liquid crystal display (PNLCD) that has a high transparency and that does not darken a field image in the optical viewfinder.
On that occasion, an information display portion using a liquid crystal is basically set to block off field light and to appear black.
Such a non-self-luminous display portion using the liquid crystal can be made luminous with illumination using LED light, as disclosed in Japanese Patent Laid-Open No. 8-313973. However, the luminance of the display portion is low because of utilizing reflected diffusion light through a liquid crystal polymer. Accordingly, the information on the display portion can visually be confirmed in a satisfactory manner only when the image-taking environment is dark.
Thus, the liquid crystal display method has the drawback that luminescence from the liquid crystal display portion cannot visually be confirmed in a relatively bright place. For example, when an object (person) wearing a black costume overlaps with the liquid crystal display portion appearing black, the information given by the liquid crystal display is very hard to visually recognize.
Japanese Patent Application Laid-Open No. 2000-180937 proposes a technique of disposing an organic electroluminescent element of self-luminous type and a liquid crystal element of non-self-luminous type together in an optical path of an optical viewfinder, the liquid crystal element being disposed on the side nearer to the object. When taking a very bright scene, or a scene including the background in the same color as that of luminescent light, the liquid crystal element is driven to block off light in the background such that representation of an image-taking enable region by the organic electroluminescent element (actually, luminous representation of an image-taking unable region) is more easily visually recognizable.
In the technique disclosed in Japanese Patent Laid-Open No. 2000-180937, however, because the image-taking unable region in a peripheral zone of a viewfinder field is displayed with luminescence of the organic electroluminescent element, a wide area including the image-taking unable region needs to be made luminous in a non-glaring, faint and uniform way. Moreover, uncomfortable sensing is basically inevitable in such a point that the image-taking unable region is displayed with higher legibility, i.e., that the image-taking unable region is displayed with luminescence to be more noticeable.
As another region display method using a self-luminous display element, e.g., an organic electroluminescent element, it is known to make luminous only a line indicating the boundary of a region to be displayed. However, such a method cannot be said as being superior in terms of a function of displaying the image-taking enable region because an object image appears similarly in both the image-taking unable region and the image-taking enable region.
For the reason described above, it is understood that, when displaying a large area, such as when displaying the image-taking enable region, better legibility is obtained by driving the liquid crystal display element to block off the light such that a photographer can view only the actual image-taking enable region.
Japanese Patent Laid-Open No. 2000-180937 discloses that the liquid crystal display element is disposed nearer to the object than the organic electroluminescent element, but it does not discuss the problem regarding what positional relationship is to be satisfied by each display element with respect to a primary image plane of an imaging lens, in particular the difference in appearance between representation of a focus detection region for auto-focusing and an object image, i.e., an optimum panel arrangement in consideration of the diopter difference among observers.
As seen from the above discussion, a novel display method is demanded which can optimally perform various kinds of information display, including the case of displaying the image-taking enable region of a camera in viewfinder display.